This invention relates to the field of card-edge connectors for plug-in board circuits.
A plug-in board (designated hereinafter as a card) has the appearance of a small plate having the shape of a quadrilateral and formed of electrically insulating material. The card is designed to support a plurality of electronic components and interconnecting leads, such leads being formed in the majority of instances by depositing a metal having good electrical conductivity on the card.
Connection with external utilization circuits is effected by means of a plurality of contacts placed on one or a number of sides of the card and adapted to cooperate with contacts of complementary shape forming part of a fixed connector which is connected to the utilization circuits. As a general rule, said connector performs a second function, namely that of serving as a mechanical support for the card in the equipment in which it is employed.
By virtue of the fact that the plug-in card has the shape of a quadrilateral, the connectors are thus endowed with the general structure of elongated blocks in the form of strips placed at right angles on a common flat base.
In one form of construction which is frequently encountered, and in particular when provision is made for four strips connectors defining a closed quadrilateral, positioning of a plug-in card for connection and fixing calls for the construction of strip connectors in two portions which are capable of relative displacement with respect to each other. This entails the need to initiate an operation in two stages: a card insertion stage corresponding to an open position of the movable portion followed by a card connecting and fixing stage corresponding to the closed position of said movable portion.
In some cases, these arrangements provide the possibility of placing a card in position by means of a single movement of translation in a direction parallel to a strip connector, in the open position which effects a withdrawal of the electric contacts and ensures frictionless insertion of the card.
However, in an increasing number of applications encountered in practice, plug-in circuits of this type utilize electric power values which are constantly becoming higher and this gives rise to the problem of dissipation of the thermal energy released by Joule effect.
In one known solution, to this problem cooling units positioned in the central region of the card, the cooling units being constituted by a block of material having good thermal conductivity and provided with fins for increasing its surface area, heat removal being performed by convection in the surrounding air.
However, a design of this type has limited heat-removal possibilities as a result of the inevitably small surface area available for the cooling unit. Furthermore, the permissible weight of this unit is also small by reason of the service requirements of high resistance of the card thus equipped both to impacts and vibrations. Finally, fixing of the cooling unit on the substrate board presents a problem which is difficult to solve by reason of the differences in thermal expansion between these two elements respectively fabricated for example from an alloy of aluminum and alumina and having very different coefficients of expansion. The methods often adopted for bonding by means of a silicone joint offer a degree of resistance which is not only of a low order but is also temporary.
Another type of solution has been proposed for utilizing the support strips themselves. Some regions of these strips are interposed between the electric-contact regions and are accordingly fitted with elements so arranged that certain surfaces of these elements are placed in thermal contact with the edges of the card to be cooled.
However, the assignment of a third function or heat-removal function to the supporting strip-connector comes up against difficulties in known forms of construction since electric and thermal connections cannot readily be obtained at the same time. The technical requirements to be satisfied for these two types of connection are in fact different and the juxtaposition of regions assigned alternately to the two functions along a single strip suffers from a certain degree of incompatibility by reason of the different contact surfaces and bearing pressures to be employed.